Mitigation of the impacts of the dynamic phase variation on the performance of GaN and LDMOS Doherty power amplifiers/transmitters

To deal with the continuously increasing number of wireless communications subscribers and the growing quest for higher data rates, modern wireless communication standards (third generation and beyond) employ spectrum efficient modulation and access techniques, such as quadratic amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM), etc. Although these techniques permit an efficient management of the overcrowded radio frequency (RF) spectrum, they also result in creating highly varying envelope signals that are characterized with high peak-to-average power ratio (PAPR). To avoid signal clipping and distortion of transmitted information, the power amplifier (PA) of wireless transmitter operates at large back-off from its saturation power level where its power efficiency drops drastically. The present work sheds the light on the phase imbalance problem and thoroughly analyses it for gallium nitride (GaN) and laterally diffused metal oxide semiconductor (LDMOS) device technologies, which are used in most of Doherty PA implementations. A number of strategies are then provided to tackle such a problem and to optimize the performance of GaN and LDMOS based Doherty PAs.